In recent years it has become popular, in the iron clubs of a set of golf clubs, to provide a central cavity in the back of each club head in order to concentrate the weight of the head around its perimeter. This concept is called "perimeter weighting". The shape and positioning of the cavity relative to the head determine the distribution of weight in the club head.
It is further known in such perimeter weighted clubs, where club head cavities are employed to produce perimeter weighting, that as club length decreases the cavity size should decrease. Thus, in the longest one iron, for example, a large cavity is used to produce the maximum perimeterization of weight. In contrast, in a shorter ten iron (pitching wedge), for example, a small cavity is used and perimeter weighting is less accentuated. In practice, the ten iron head is considerably heavier than the one iron head; as much as 25%, for example.